Plasmodium vivax malaria, a leading health problem throughout the Amazon basin on Latin America, is endemic in the Peruvian Amazon. The long-term goal of this project is to determine specific epidemiological characteristics of P. vivax transmission and human reservoirs of maintaining P. vivax transmission in the Peruvian Amazon region towards the rational deployment of a transmission-blocking vaccine. This project will test the hypothesis that reproduction of exogenous P. vivax into local populations is responsible for continuing transmission in rural villages surrounding Iquitos, Peru, the capital of the Peruvian Amazon. Alternative hypotheses are 1) that relapsing P. vivax malaria is the source for maintaining local transmission;or 2) there is simply continuous transmission of already locally established genotypes within local populations. Specific aim 1 is to determine circulating Plasmodium vivax genotypes at the individual village level through prospective, population-based surveillance of people with P. vivax parasitemia. Changes or stability of P. vivax genotypes will be assessed over space and time using recently validated genetic markers. Specific aim 2 is to determine transmission dynamics of P. vivax using geographic spatio- temporal analysis of circulating genotypes using spatial statistical modeling and cluster analysis. These analyses will distinguish whether circulating P. vivax genotypes are already established in villages (either continuously circulating or resulting from relapsing P. vivax from hypnozoites) or are newly introduced by infected inhabitants returning from travel away from the village. Specific aim 3 is to determine whether transmission-blocking immunity develops in the Peruvian Amazon population to potentially modify P. vivax transmission dynamics. Membrane feeding studies will be performed using local Anopheles darlingi mosquitoes and local P. vivax patients as sources of parasites, and by experimental infections of Anopheles mosquitoes from splenectomized non-human primates infected experimentally with P. vivax. In vitro assays (ELISA, IFA) will be used to determine the validity of the in vivo mosquito infection assay. These data will provide the basis for planning transmission-blocking interventions and elimination of human reservoirs of P. vivax, and provide a rational basis for determining strategies to implement and deploy new transmission- blocking vaccines as one approach towards the future elimination of P. vivax malaria from the Amazon basin.